In recent years, as considerable attention has been focused on environmental issues facing the earth, the reduction of nitrogen oxides (NOx) has been identified as one important issue, and is an issue requiring urgent attention. Among methods of reducing NOx, technology for inhibiting generation of NOx is very important, and techniques such as exhaust gas recirculation, lean burn combustion, thick and thin fuel combustion, and staged combustion are already known, and are being widely employed in industrial applications through to consumer applications. Although NOx countermeasures have progressed to some degree through application of low NOx combustors that apply these techniques, more effective methods of further reducing NOx are still being sought.
Among methods that aim to address the issues described above, one example of a method of reducing NOx that is the subject of ongoing research and development is a method of performing a type of timed thick and thin fuel combustion in which the flow rates of the fuel and the oxidant are changed periodically (hereafter referred to as “forced oscillating combustion”) (see Patent Documents 1 to 6).
In this method, by oscillating control of the supply flow rate of either the fuel or the oxidant, or both the fuel and the oxidant, the stoichiometric ratio of the combustion flame is altered to generate alternating fuel-rich combustion and fuel-lean combustion, thereby achieving a reduction in the emission of NOx.
Further, Patent Document 7 discloses a method of reducing NOx that utilizes a pulsed combustion in which the oxidant is enriched using pure oxygen, so-called “forced oscillating combustion”, as well as an apparatus for implementing this method.
Furthermore, Patent Documents 8 to 14 disclose so-called staged combustion methods in which the fuel and/or the oxidant are jetted into the furnace or combustion chamber in multiple stages, and also mention many effects of low NOx methods.